Generally, it is well known that the output performance of an engine according to the revolutions of the engine depends upon the length of intake passage formed in the intake manifold, that is, in case that the intake passage is made long, the output performance of the engine at low speed is raised due to the pulse effect of air, and where the intake passage is made short, the output performance of the engine at high speed is enhanced due to the inertia force of air.
Thus, there has been proposed an intake apparatus of an engine which is capable of enhancing the output performance of the engine by making the length of the intake passage of the intake manifold changeable and changing the length of the intake passage in accordance with the change of revolutions of the engine.
In a conventional intake apparatus, as shown in FIG. 2, both a short intake passage 4 and a long intake passage 5 are separately provided within an intake manifold 1 to form intake passages each of which extends from an intake section 2 to an intake port of an engine 3, and an intake control valve 6 is installed in the course of the short intake passage 4 in such a manner that the intake control valve 6 may be switched to close or open the intake passage 4 in accordance with the revolutions of the engine 3, thereby to allow air to flow into the engine 3 through the short intake passage 4 or the long intake passage 5. However, such a conventional intake apparatus has defects in that the long intake passage 5 is largely outwardly bent between the intake section 2 and the engine 3, and therefore the volume of the apparatus as a whole is bulky, and in that the quick response to rapid acceleration or rapid deceleration of an automobile deteriorates.
Meanwhile, the intake control valve 6 is, as shown in FIGS. 1 and 3, secured to a shaft 9 by means of, for instance, screws 8, and the shaft 9 is actuated by an actuator (not shown) in response to the operating condition of the engine so as to switch the intake control valve 6 between the long intake passage 5 and the short intake passage 4, thereby to allow air to flow from the intake section 2 into the engine through the long intake passage 4 or the short intake passage 5.
However, where the conventional shaft 9 shown in FIG. 1 is thermally expanded due to high temperature of engine, the intake control valve 6 contacts and interferes with the inner surface of the intake manifold 1, and as a result, the intake control valve 6 does not operate smoothly. Also, the conventional apparatus is disadvantageous in that a driving mechanism for driving the shaft is complex.